This invention relates generally to packaging of electronic components and, more specifically, to assemblies of dual printed circuit boards (PCBs). In many electronics systems, such as avionics systems, electronic modules are packaged on printed circuit boards having edge connectors for plugging into a larger board known as a backplane or a mother board. The PCB modules are oriented parallel with each other and perpendicular to the backplane.
In one conventional form of this arrangement, the PCB modules are assembled in pairs, each forming a dual PCB module with a single connector at one edge of the module. The conventional technique for pakaging dual PCB modules is to mount them back to back on a common frame providing both structural and thermal functions. In other words, the frame functions both as a structural support and as a thermal conductor to dissipate heat generated in the modules, transmitting it to a larger frame in the system. The circuit components must usually be protected from the environment in which they are used. Therefore, the use of a common central frame usually requires that separate covers be mounted over each of the PCBs, which typically have components of various heights projecting above board level. The need for separate covers increases the module thickness, which results in lower overall component packing density. Moreover, the covers contribute little to the structural and thermal integrity of the assembly, and testing and maintenance of the modules is rendered much more difficult.
Another difficulty with dual PCB modules of the prior art results from a requirement for connections between boards, as well as from the boards to the backplane. In part, this requirement arises from a limited backplane capacity to handle input and output signals to and from the boards. Some of these signals are, therefore, routed from one board to another before reaching the backplane. In the past, these intramodule connections have been established by means of a special connector assembly or a flexible printed-circuit connector at the "top" edge of the boards, opposite the "bottom" edge where a backplane connector is located. Obviously, the terms "top" and "bottom" are used only for convenience. The orientation of the backplane and circuit boards is not limited.
This arrangement for intramodule connection increases the complexity of conductor routing on the boards, increases some input/output circuit lengths, and may reduce the amount of board area or "real estate" available for components on the boards. In addition, the dual module made in this manner is difficult to test and maintain, since access to the backs of the circuit boards is precluded after installation of the inter-board connector at the top edge of the module.
It will be appreciated that there is a need for an improved dual PCB module. Ideally, the structure should maintain structural and thermal integrity, but should minimize circuit complexity and permit easy access for testing and maintenance. The present invention satisfies these needs.